CA1063589A - Alkylation catalyst recovery process - Google Patents
Alkylation catalyst recovery processInfo
- Publication number
- CA1063589A CA1063589A CA235,599A CA235599A CA1063589A CA 1063589 A CA1063589 A CA 1063589A CA 235599 A CA235599 A CA 235599A CA 1063589 A CA1063589 A CA 1063589A
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- Prior art keywords
- fluoride
- acid
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- conducted
- catalyst
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J27/00—Catalysts comprising the elements or compounds of halogens, sulfur, selenium, tellurium, phosphorus or nitrogen; Catalysts comprising carbon compounds
- B01J27/28—Regeneration or reactivation
- B01J27/32—Regeneration or reactivation of catalysts comprising compounds of halogens
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- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Organic Chemistry (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Catalysts (AREA)
- Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A process for removal of fluoride compounds from spent alkylation catalyst containing fluorosulfonic acid and sulfuric acid wherein hydrogen fluoride and fluorosulfonic acid, in the presence of water, are removed by vacuum dis-tillation following which the remaining sulfuric acid rich fraction of the spent catalyst is reacted with a silica con-taining material to convert most of the remaining residual hydrogen fluoride to silicon fluoride which is volatilized from the mixture to thereby provide a sulfuric acid effluent free of substantial amounts of fluoride compounds. The hydrogen fluoride recovered is reacted with sulfur trioxide to form fresh fluorosulfonic acid which is combined with sulfuric acid to provide fresh alkylationa catalyst.
A process for removal of fluoride compounds from spent alkylation catalyst containing fluorosulfonic acid and sulfuric acid wherein hydrogen fluoride and fluorosulfonic acid, in the presence of water, are removed by vacuum dis-tillation following which the remaining sulfuric acid rich fraction of the spent catalyst is reacted with a silica con-taining material to convert most of the remaining residual hydrogen fluoride to silicon fluoride which is volatilized from the mixture to thereby provide a sulfuric acid effluent free of substantial amounts of fluoride compounds. The hydrogen fluoride recovered is reacted with sulfur trioxide to form fresh fluorosulfonic acid which is combined with sulfuric acid to provide fresh alkylationa catalyst.
Description
~ \
`- 1063589 BACKGROUND OF THE INVENTION
The present invention relates to a catalyst re-covery process. More particularly, the present invention relates to a process for the removal of fluoride compounds from spent alkylation catalysts comprised of fluorosulfonic acid and sulfuric acid, and to the regeneration of fresh alkylation catalyst.
; Liquid phase alkylation processes wherein an isoparaffin hydrocarbon, such as isobutane, isopentane, etc.
are alkylated with olefin hydrocarbons such as propylene, butylenes, etc. for the production of alkylate products com-prising highly branched C7-C8 range paraffin hydrocarbons having high octane value, are well known and widely practiced.
In such processes, the reactant hydrocarbons are usually con-tacted in the liquid phase, at elevated temperatures in the presence of acid alkylation catalysts and under conditions of good mixing, reaction pressures usually being only suffi-cient to maintain the reactants in the liquid phase.
; Although numerous acid catalysts may be employed -~
in such alkylation processes, an effective catalyst com-prises a mixture of sulfuric acid and fluorosulfonic acid. -One such catalyst, particularly effective in the alkylation processes under consideration is disclosed United States Patent 3,922,319. The novel alkylation catalyst disclosed in the aforementioned application comprises fluorosulfonic acid and sulfuric acid in a weight ratio of from about 0.11/1 -~
to about 0.32/1, respectively, the catalyst having a titrat-able acidity in the range of 16.6 to 21 milli-equivalents per gram (meg/gm) and which may contain up to 3% by weight .' ~ ~
1(~63~89 water and up to 10% by weight acid oils, the acid oils com-prising relatively high molecular weight reaction products of sulfuric acid and hydrocarbons present in the process. -In the process described in the aforementioned patent a C4-C6 isoparaffin hydrocarbon such as isobutane is contacted with a C3-C5 olefin hydrocarbon such as propy-; lene, a butylene, or mixtures thereof, in a molar ratio of -~
- isoparaffin to olefin of from about 2/1 to 20/1, in the liquid phase, in the presence of the alkylation catalyst at a temperature in the range of from about 0F. to about 100F.
Reaction pressures employed may range from ambient to super-atmospheric, the pressure employed generally being sufficient to maintain the hydrocarbon reactants in the liquid phase.
Since the reactants may be normally gaseous at alkylation reaction temperatures, reaction pressures generally range from about 10 to about 150 psig. Preferably, the alkylation reaction mixture is subjected to good mixing to form a hydro-~ carbon in continuous acid phase emulsion which comprises - from about 40 to about 70 volume % acid phase and from about 60 to about 30 volume % hydrocarbon phase. Liquid volume ratios of isoparaffin hydrocarbons to olefin hydrocarbons of from about 2/1 to about 20/1 are generally employed in the process. Contact times for hydrocarbon reactants in the alkylation zone, in the presence of the alkylation catalyst, may range from about 0.5 to about 60 minutes. Preferably, the contact time is sufficient to ensure essentially complete conversion of olefin reactant in the alkylation zone. Such contact times are sufficient for providing an olefin space velocity in the range of about 0.1 to about 1.0 volumes olefin/hour/volume of catalyst. The process may be conducted :
1~63~89 batchwise or continuously. It has been found that use of the catalyst described in the aforementioned patent in alkylating C4-C6 isoparaffin with a C3-C5 mono-olefin, produces an alk~late of increased octane values over that obtained by prior art catalysts.
When using the above-described fluorosulfonic-sulfuric acid alkylation catalyst, or for that matter, any sulfuric acid alkylation catalyst containing a similar fluoro acid, it is common practice to process the spent catalyst in such a fashion so as to regenerate fresh sulfuric acid, the major component of the catalyst. However, even though the fluorosulfonic acid is present as a minor component in the alkylation catalyst, because of its expense relative to that of sulfuric acid, it is desirable to recover, as well, the fluorosulfonic acid or any fluoro compounds which can be easily converted to the fluorosulfonic acid.
One method for recovering the sulfuric acid from the spent alkylation catalyst is to treat the spent catalyst in what is known as a sludge conversion unit. In such a unit - 20 the spent catalyst containing water and organic materials is charged to a furnace for oxidative conversion of all the sulfuric species present to sulfur dioxide. The sulfur dioxide, in admixture with air, is then passed over a catalyst, e.g.
V2O5 or some other such suitable oxidation catalyst, in a converter section of the unit to form SO3. The SO3 is then absorbed in a sulfuric acid solution to produce oleum which is then diluted with water to produce sulfuric acid of the .. :
desired concentration, i.e. 97-99 weight %, for the alkyl-ation catalyst. The furnaces used in such slude conversion units employ refractories which are readily attacked by HF
.
. ~
1063589 . ~
or HF precursors such as fluorosulfonic acid. For example, to prevent damage to refractory furnace linings, fluoride concentrations (calculated as HF) of about 10 ppmw or less are particularly desirable. At levels above about 10 ppmw, fluoride attack upon refractory lining is accelerated, thus shortening the operating lifetime of such materials in the sludge conversion unit. Over and above the potential damage to the refractories in the furnace, any HF in the converter section would volatilize the vanadium from the V205 oxidation catalyst. Accordingly, a process which effectively recovers the fluorosul-fonic acid or precursors thereof from the spent catalyst and also provides a feed to the sludge conversion unit substantially free of damaging fluoro compounds is highly desirable.
SUMMARY OF THE INVENTICN
According to one aspect of the invention a process for the removal of fluoride compounds from spent alkylation catalyst containing fluorosulfon-ic acid and sulfuric acid comprising: la) subjecting said spent catalyst to distillation, at atmospheric pressure or below, in a temperature range of from about 50 to about 120 C. and in admixture with at least the stoichometric amount of water necessary to hydrolyze said fluorosulfonic acid to hydrogen fluoride; (b) recovering a first fraction from said distillation, said first fraction comprising primarily hydrogen fluoride; (c) recovering a second fraction from said distillation, said second fraction comprising residual hy-drogen fluoride and the greater part of said sulfuric acid present in said spent catalyst; (d) contacting, in a reaction zone, said second fraction with a silica containing material in an amount and for a period of time sufficient to react at least a portion of said residual hydrogen fluoride with said silica to form silicon fluoride; (e) volatilizing said silicon fluoride from said reaction zone; and (f) recovering from said reaction zone an effluent acid fraction containing the greater part of said sulfuric acid present in said spent catalyst and being free of substantial amounts of fluoride com-~ ~ - 4 -:- .
1063589 ::
pounds.
According to a further aspect of the invention a~process for the regeneration of spent alkylation catalyst containing fluorosulfonic acid and -~
sulfuric acid comprising: (a) subjecting said spent catalyst to distilla-tion, at atmospheric pressure or below, in a temperature range of from about 50 to about 120 C. and in admixture with at least the stoichometric amount of water necessary to hydrolyze said fluorosulfonic acid to hydrogen fluoride;
(b) recovering a first fraction from said distillation, said first fraction comprising primarily hydrogen fluoride; (c) treating said first fraction with sulfur trioxide to form regenerated fluorosulfonic acid from said hydro-gen fluoride present in said first fraction; (d) recovering a second frac-tion from said distillation, said second fraction comprising residual hydro-gen fluoride and the greater part of said sulfuric acid present in said spent catalyst; (e) contacting, in a reaction zone, said second fraction with a silica containing material in an amount and for a period of time sufficient to react at least a portion of said residual hydrogen fluoride with said silica to form silicon fluoride; (f) volatilizing said silicon fluoride from said reaction zone; (g) recovering from said reaction zone an effluent acid ~ ~-fraction containing the greater part of said sulfuric acid present in said spent catalyst and being free of substantial amounts of fluoride compounds;
(h) combusting said effluent acid fraction to convert said sulfuric acid ... .
to sulfur dioxide; (i) converting at least a portion of said sulfur dioxide to sulfur trioxide; (j) converting at least a portion of said sulfur tri-oxide from step (i) into regenerated sulfuric acid; and (k) combining said regenerated sulfuric acid with said regenerated fluorosulfonic acid to pro-duce fresh alkylation catalyst.
In one embodiment of the present invention, the spent alkylation catalyst, comprised of fluorosulfonic acid and sulfuric acid, is subjected to a two-stage process to effect removal of most of the fluoride compounds - 4a -:
-~ :
`` 1063589 from the spent catalyst so as to provide an acid effluent free of substantial amounts of fluoride compounds and suitable as a feed to a sludge conversion unit. In the first stage of the dual stage process, the spent catalyst is subjected to separation in a distillation zone. The distillation is conduct-ed at atmospheric pressure or below in a temperature range of from about 50 to about 120C. and in admixture with at least the stoichometric amount of .
water necessary to hydrolyze the fluorosulfonic acid in the spent catalyst .1 to hydrogen fluoride. A vapor or first fraction comprising primarily hydro- -gen fluoride mixed with some ' ' .;~
,,1 , ., .
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. ~
' :, - 4b -. ~
. ' ~ ' ' ' ' : ' , .
.'' .
~063589 fluorosulfonic acid and SO2 is recovered from the distilla-tion zone for further processing. In the second stage of the process, a second fraction recovered from the distilla-tion zone and comprising the fraction of the spent catalyst remaining after removal of the ~irst fraction is contacted, in a reaction zone, with a silica containing material such as sand, silica gel, etc., in an amount and for a period of time sufficient to effect reaction of the bulk of the resi-dual hydrogen fluoride with the silica to form more volatile silicon fluoride (SiF4) which is volatilized from the reaction zone. An acid effluent, free of substantial amounts of ; fluoro compounds, containing substantially all of the sulfuric acld present in the spent acid, and suitable for charging to a sludge conversion unit is then recovered from the reaction zone.
In another embodiment of the present invention, the above-described fluoro compound removal process is em-ployed as part of an alkylation catalyst regeneration process.
The hydrogen fluoride removed in the first stage is reacted with SO3 to form fluorosulfonic acid. Additionally, the acid effluent from the second stage is treated in the sludge conversion unit to ultimately produce fresh sulfuric acid which is then combined with the fluorosulfonic acid obtained .. . .
from the first stage of the process to produce fresh alkyla-tion catalyst.
BRIEF DESCRIPTION OF THE DRAWINGS
The single figure is a schematic flow diagram of the process of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Reference is now made to the accompanying draw-ing for a more detailed description of the process of the . .
1063~89 .
present invention.
Spent catalyst ~rom alkylation unit 10 passes via line 11 into distillation zone 12, the primary treatment ¦ stage of the process. The spent catalyst from alkylation unit 10 comprises primarily sulfuric acid (about 88 - 90%
by weight) and contains in addition, fluorosul~onic acid, (~ 15% by volume) water (3 - 4% by weight), acid oils, sul-fonated and fluorinated organic materials and other side reaction products formed in the alkylation reaction. Gen-erally, the total fluoride content, measured as HF, is in the range of 15,000 to 30,000 ppmw (parts per million weight)O
Distillation zone 12 is preferably operated at atmospheric pressure or below and elevated temperatures of from about 50 to about 120C. It is desirable that the distillation apparatus be of a type which can generate a large surface area of spent catalyst, one such type of preferred apparatus being a multi-stage agitated vacuum digester.
As noted above, the distillation is conducted in the presence of at least the stoichometric amount of water needed to hydrolyze the fluorosulfonic acid to hydrogen fluoride. Generally speaking, in spent alkylation catalyst the water content is from 3 to 4% by weight. Thus, in a typical spent alkylation catalyst, it is not necessary to add water to effect hydrolysis of all of the fluorosulfonic acid in the spent catalyst. As will be seen hereafter, how-ever, conducting the distillation in the presence of a stoichometric excess of water, e.g. up to 15% by weight of the spent catalyst, greatly enhances fluoride removal in the distillation zone. Accordingly, provision can be made for adding water to distillation zone 12 via line 26.
.
1063~89 -A lightJ substantially vapor fraction comprising primarily hydrogen fluoride, some fluorosulfonic acid and a small amount of S02 formed from oxidative side reactions flashes and is removed from distillation zone 12 via line 13.
The hydrogen fluoride in the fraction removed via line 13 results not only from the hydrogen fluoride originally pres-ent in the spent catalyst and that formed by hydrolysis of the fluorosulfonic acid, but in addition, arises from de-composition of alkyl fluorosulfonates and other organofluoro compounds formed in the alkylation reaction.
A second, heavier fraction comprising the resi-dual material from zone 12 and containing substantially all of the sulfuric acid present in the spent catalyst, plus residual hydrogen fluoride (preferably C lO0 ppmw HF), acid oils, water and other impurities is removed from distilla-tion zone 12 via line 14 and transferred to reaction zone 15. Reaction zone 15 is the secondary treatment stage of ` the process and conveniently employs a vessel, preferably agitated, into which is introduced a particulate silica con- -taining material via line 16. In reaction zone 15, which is preferably operated at elevated temperatures and sub-atmos-pheric pressure, the residual hydrogen fluoride present in the spent catalyst fractlon removed from distillation zone 12, reacts with the silica to form silicon fluoride. Silicon, fluoride belng more volatile than HF, is relatively easily separated from the mixture in zone 15. A substantially vapor fraction containing the silicon fluoride thus produced is removed via line 29 for disposal. Any non-reactive solids introduced wlth the silica containing material are removed from the reaction zone 15 via line 17 and sent to waste.
:
: 1063589 ,' :
An acid effluent stream containing substantially all of the sulfuric acid present in the spent catalyst and preferably having a fluoride content, as HF, of c 10 ppmw is removed from reaction zone 15 via line 18 and fed to sludge conversion unit 19. In sludge conversi~n unit 19, the spent catalyst, having a greatly reduced ~luoride con-tent, is combusted in a suitable furnace under conditions such that all the sulfur species present in the catalyst are converted to sulfur dioxide. The sludge conversion unit fur-. ,.,.~
ther contains a converter section employing an oxidation catalyst such as V205 which, in the presence of air, converts ; the S02 into S03. Part of the S03 thus produced is absorbed in a fresh sulfuric acid solution to form oleum which is then diluted with water to form 97 - 99 weight ~ sulfuric acid.
The ~ulfuric acid thus produced is removed via line 20 for recycle to alkylation unit 10.
The light fraction removed from zone 12 via line 13 and comprising hydrogen fluoride, fluorosulfonic acid and S02, is introduced into fluorosulfonic acid regeneration unit 27 and combined with S03 to convert the HF to additional fluorosulfonic acid. A portion of the S03 in unit 27 may be obtained from unit 19 via line 22. Any additional S03 needed to convert the hydrogen fluoride to fluorosulfonic acid can be obtained from S03 make-up stream 23. The regen-; erated fluorosulfonic acid stream exits unit 27 via line 28.
The S02 present in the fluorosulfonic acid stream is removed from line 28 via line 24 to provide a stream comprising sub-stantially fluorosulfonic acid. The fluorosulfonic acid is then combined with the sulfuric acid from line 20 in the proper proportions to form fresh alkylation catalyst which .~: ~ ' . ' - . .
' ' ~
is fed to alkylation unit 10 via line 25. -While reference has been made to the use of a multi-stage stirred vacuum digester in distillation zone 12, it is to be understood that other types of equipment can be employed. The purpose of the primary treatment stage or distillation zone is to remove the relatively volatile hydrogen fluoride from the spent catalyst. Thus, any means which will provide a large surface area of spent catalyst to allow efficient flashing of the hydrogen fluoride can be used. For example, rotary film evaporators, packed trickle -towers, spray towers, baffle towers, rotary disc contactors, etc. can be employed.
Preferably, the distillation zone, i.e. the pri-mary treatment stage, comprises distillation at atmospheric pressure or below and at elevated temperatures. Pressures in the distillation zone should be as low as economically prac-tical and preferably below about 1 psia. Temperatures will, of course, depend on the pressures, but generally will range from about 50 to about 120C., and preferably from about ~-80 to 110C. It has been found that if the spent alkylation catalyst is sub~ected to temperatures of 125C. or higher for e~tended periods of time, the catalyst tends to thicken to a semi-solid mass. Thus, the temperatures should be .,, kept below about 125C. For a typical spent alkylation catalyst containing 20,000 to 30,000 ppmw fluoride as HF, it has been found that if the distillation zone is maintained . . .
at a temperature of around 100C. and a pressure of about or below 1 psia, and under conditions affording increased surface a~b-aiof thb spent catalyst, 90% recovery~ by weight, 3 of the fluoride (calculated as HF) can be achieved without : g :.
' ~ .
. ~ ~
1063~89 adverse degradation side reactions which occur at higher temperatures.
The residence time in the distillation zone will vary depending on pressure, temperature, fluoride content of the spent acid, water content, etc. Generally speaking, the residence time of the spent catalyst in the distillation zone should be sufficient to permit maximum hydrolysis of the fluorosulfonic acid to hydrogen fluoride and subsequent flashing of the hydrogen fluoride and/or remaining fluoro-sulfonic acid from the distillation zone. Additionally, relatively long residence times in the distillation zone promote the decomposition of organofluoro compounds in the spent catalyst into hydrogen fluoride and/or fluorosulfonic acid thereby maximizing the recovery of the fluorosulfonic acid for recycle to the alkylation unit and minimizing the fluoride removal needed in the second stage of the process.
However, while long residence times increase the fluoride recovery from the spent catalyst in the distilla-tion zone, there is also a concomitant increase in the amount Of S02 recovered in the vapor fraction with the hydrogen fluoride. Since S02 losses represent loss of sulfur for regeneration into fresh sulfuric acid, minimum digestion or residence time in the distillation zone consistent with adequate fluoride removal should be used so as to minimize such losses. In general, it has been found that at a tem-perature of about 100C. and a pressure of about 1 psia or lower, a residence time of 4 hours or greater wlll effect -~ removal of 90% by weight of the total fluoride, calculated as HF, from a typical spent catalyst, i.e. containing 20,000 _ 30,000 ppmw fluoride. In such a typical spent catalyst, .
1063~89 if the digestion time is increased to ~ hours or greater, as for example, from about 6 to about 8 hours, greater fluoride removal (about 97% by weight) can be obtained, e.g. from about 23,000 ppmw to about 700 - 800 ppmw. It has also been found that if the spent catalyst has a rela-tively low initial fluoride concentration, e.g. about 1000 - 1500 ppmw, calculated as HF, the fluoride level can be reduced to 74 ppmw after 2 hours and 33 ppmw after 8 hours.
With ample residence time and at a temperature of around 100C. and a pressure of 5 - 15 mm. Hg, the fluoride content (as HF) of a typical spent acid catalyst can be reduced to 100 ppmw or less.
While the distillation step of the process of the present invention can be conducted in the presence of the amount of water needed to stoichometrically react with the fluorosulfonic acid to form hydrogen fluoride, it has been found that higher water content in the spent catalyst greatly improves fluoride recovery in the distillation zone.
As noted, typical spent catalyst contains 3 - 4% by weight water which is sufficient, as noted above, to effect good - recovery of fluoride from spent catalyst in the distillation zone. However, when the water content of the spent catalyst contains up to 8% by weight water, and more preferably from about 8 to about 15% by weight water, the volatility of the fluorides in the s~ent acid is greatly increased. Apparently, - the excess water is needed to (1) force the hydrolysis of the fluorosulfonic acid to HF which is more volatile, and/or
`- 1063589 BACKGROUND OF THE INVENTION
The present invention relates to a catalyst re-covery process. More particularly, the present invention relates to a process for the removal of fluoride compounds from spent alkylation catalysts comprised of fluorosulfonic acid and sulfuric acid, and to the regeneration of fresh alkylation catalyst.
; Liquid phase alkylation processes wherein an isoparaffin hydrocarbon, such as isobutane, isopentane, etc.
are alkylated with olefin hydrocarbons such as propylene, butylenes, etc. for the production of alkylate products com-prising highly branched C7-C8 range paraffin hydrocarbons having high octane value, are well known and widely practiced.
In such processes, the reactant hydrocarbons are usually con-tacted in the liquid phase, at elevated temperatures in the presence of acid alkylation catalysts and under conditions of good mixing, reaction pressures usually being only suffi-cient to maintain the reactants in the liquid phase.
; Although numerous acid catalysts may be employed -~
in such alkylation processes, an effective catalyst com-prises a mixture of sulfuric acid and fluorosulfonic acid. -One such catalyst, particularly effective in the alkylation processes under consideration is disclosed United States Patent 3,922,319. The novel alkylation catalyst disclosed in the aforementioned application comprises fluorosulfonic acid and sulfuric acid in a weight ratio of from about 0.11/1 -~
to about 0.32/1, respectively, the catalyst having a titrat-able acidity in the range of 16.6 to 21 milli-equivalents per gram (meg/gm) and which may contain up to 3% by weight .' ~ ~
1(~63~89 water and up to 10% by weight acid oils, the acid oils com-prising relatively high molecular weight reaction products of sulfuric acid and hydrocarbons present in the process. -In the process described in the aforementioned patent a C4-C6 isoparaffin hydrocarbon such as isobutane is contacted with a C3-C5 olefin hydrocarbon such as propy-; lene, a butylene, or mixtures thereof, in a molar ratio of -~
- isoparaffin to olefin of from about 2/1 to 20/1, in the liquid phase, in the presence of the alkylation catalyst at a temperature in the range of from about 0F. to about 100F.
Reaction pressures employed may range from ambient to super-atmospheric, the pressure employed generally being sufficient to maintain the hydrocarbon reactants in the liquid phase.
Since the reactants may be normally gaseous at alkylation reaction temperatures, reaction pressures generally range from about 10 to about 150 psig. Preferably, the alkylation reaction mixture is subjected to good mixing to form a hydro-~ carbon in continuous acid phase emulsion which comprises - from about 40 to about 70 volume % acid phase and from about 60 to about 30 volume % hydrocarbon phase. Liquid volume ratios of isoparaffin hydrocarbons to olefin hydrocarbons of from about 2/1 to about 20/1 are generally employed in the process. Contact times for hydrocarbon reactants in the alkylation zone, in the presence of the alkylation catalyst, may range from about 0.5 to about 60 minutes. Preferably, the contact time is sufficient to ensure essentially complete conversion of olefin reactant in the alkylation zone. Such contact times are sufficient for providing an olefin space velocity in the range of about 0.1 to about 1.0 volumes olefin/hour/volume of catalyst. The process may be conducted :
1~63~89 batchwise or continuously. It has been found that use of the catalyst described in the aforementioned patent in alkylating C4-C6 isoparaffin with a C3-C5 mono-olefin, produces an alk~late of increased octane values over that obtained by prior art catalysts.
When using the above-described fluorosulfonic-sulfuric acid alkylation catalyst, or for that matter, any sulfuric acid alkylation catalyst containing a similar fluoro acid, it is common practice to process the spent catalyst in such a fashion so as to regenerate fresh sulfuric acid, the major component of the catalyst. However, even though the fluorosulfonic acid is present as a minor component in the alkylation catalyst, because of its expense relative to that of sulfuric acid, it is desirable to recover, as well, the fluorosulfonic acid or any fluoro compounds which can be easily converted to the fluorosulfonic acid.
One method for recovering the sulfuric acid from the spent alkylation catalyst is to treat the spent catalyst in what is known as a sludge conversion unit. In such a unit - 20 the spent catalyst containing water and organic materials is charged to a furnace for oxidative conversion of all the sulfuric species present to sulfur dioxide. The sulfur dioxide, in admixture with air, is then passed over a catalyst, e.g.
V2O5 or some other such suitable oxidation catalyst, in a converter section of the unit to form SO3. The SO3 is then absorbed in a sulfuric acid solution to produce oleum which is then diluted with water to produce sulfuric acid of the .. :
desired concentration, i.e. 97-99 weight %, for the alkyl-ation catalyst. The furnaces used in such slude conversion units employ refractories which are readily attacked by HF
.
. ~
1063589 . ~
or HF precursors such as fluorosulfonic acid. For example, to prevent damage to refractory furnace linings, fluoride concentrations (calculated as HF) of about 10 ppmw or less are particularly desirable. At levels above about 10 ppmw, fluoride attack upon refractory lining is accelerated, thus shortening the operating lifetime of such materials in the sludge conversion unit. Over and above the potential damage to the refractories in the furnace, any HF in the converter section would volatilize the vanadium from the V205 oxidation catalyst. Accordingly, a process which effectively recovers the fluorosul-fonic acid or precursors thereof from the spent catalyst and also provides a feed to the sludge conversion unit substantially free of damaging fluoro compounds is highly desirable.
SUMMARY OF THE INVENTICN
According to one aspect of the invention a process for the removal of fluoride compounds from spent alkylation catalyst containing fluorosulfon-ic acid and sulfuric acid comprising: la) subjecting said spent catalyst to distillation, at atmospheric pressure or below, in a temperature range of from about 50 to about 120 C. and in admixture with at least the stoichometric amount of water necessary to hydrolyze said fluorosulfonic acid to hydrogen fluoride; (b) recovering a first fraction from said distillation, said first fraction comprising primarily hydrogen fluoride; (c) recovering a second fraction from said distillation, said second fraction comprising residual hy-drogen fluoride and the greater part of said sulfuric acid present in said spent catalyst; (d) contacting, in a reaction zone, said second fraction with a silica containing material in an amount and for a period of time sufficient to react at least a portion of said residual hydrogen fluoride with said silica to form silicon fluoride; (e) volatilizing said silicon fluoride from said reaction zone; and (f) recovering from said reaction zone an effluent acid fraction containing the greater part of said sulfuric acid present in said spent catalyst and being free of substantial amounts of fluoride com-~ ~ - 4 -:- .
1063589 ::
pounds.
According to a further aspect of the invention a~process for the regeneration of spent alkylation catalyst containing fluorosulfonic acid and -~
sulfuric acid comprising: (a) subjecting said spent catalyst to distilla-tion, at atmospheric pressure or below, in a temperature range of from about 50 to about 120 C. and in admixture with at least the stoichometric amount of water necessary to hydrolyze said fluorosulfonic acid to hydrogen fluoride;
(b) recovering a first fraction from said distillation, said first fraction comprising primarily hydrogen fluoride; (c) treating said first fraction with sulfur trioxide to form regenerated fluorosulfonic acid from said hydro-gen fluoride present in said first fraction; (d) recovering a second frac-tion from said distillation, said second fraction comprising residual hydro-gen fluoride and the greater part of said sulfuric acid present in said spent catalyst; (e) contacting, in a reaction zone, said second fraction with a silica containing material in an amount and for a period of time sufficient to react at least a portion of said residual hydrogen fluoride with said silica to form silicon fluoride; (f) volatilizing said silicon fluoride from said reaction zone; (g) recovering from said reaction zone an effluent acid ~ ~-fraction containing the greater part of said sulfuric acid present in said spent catalyst and being free of substantial amounts of fluoride compounds;
(h) combusting said effluent acid fraction to convert said sulfuric acid ... .
to sulfur dioxide; (i) converting at least a portion of said sulfur dioxide to sulfur trioxide; (j) converting at least a portion of said sulfur tri-oxide from step (i) into regenerated sulfuric acid; and (k) combining said regenerated sulfuric acid with said regenerated fluorosulfonic acid to pro-duce fresh alkylation catalyst.
In one embodiment of the present invention, the spent alkylation catalyst, comprised of fluorosulfonic acid and sulfuric acid, is subjected to a two-stage process to effect removal of most of the fluoride compounds - 4a -:
-~ :
`` 1063589 from the spent catalyst so as to provide an acid effluent free of substantial amounts of fluoride compounds and suitable as a feed to a sludge conversion unit. In the first stage of the dual stage process, the spent catalyst is subjected to separation in a distillation zone. The distillation is conduct-ed at atmospheric pressure or below in a temperature range of from about 50 to about 120C. and in admixture with at least the stoichometric amount of .
water necessary to hydrolyze the fluorosulfonic acid in the spent catalyst .1 to hydrogen fluoride. A vapor or first fraction comprising primarily hydro- -gen fluoride mixed with some ' ' .;~
,,1 , ., .
''''.' .
. ~
' :, - 4b -. ~
. ' ~ ' ' ' ' : ' , .
.'' .
~063589 fluorosulfonic acid and SO2 is recovered from the distilla-tion zone for further processing. In the second stage of the process, a second fraction recovered from the distilla-tion zone and comprising the fraction of the spent catalyst remaining after removal of the ~irst fraction is contacted, in a reaction zone, with a silica containing material such as sand, silica gel, etc., in an amount and for a period of time sufficient to effect reaction of the bulk of the resi-dual hydrogen fluoride with the silica to form more volatile silicon fluoride (SiF4) which is volatilized from the reaction zone. An acid effluent, free of substantial amounts of ; fluoro compounds, containing substantially all of the sulfuric acld present in the spent acid, and suitable for charging to a sludge conversion unit is then recovered from the reaction zone.
In another embodiment of the present invention, the above-described fluoro compound removal process is em-ployed as part of an alkylation catalyst regeneration process.
The hydrogen fluoride removed in the first stage is reacted with SO3 to form fluorosulfonic acid. Additionally, the acid effluent from the second stage is treated in the sludge conversion unit to ultimately produce fresh sulfuric acid which is then combined with the fluorosulfonic acid obtained .. . .
from the first stage of the process to produce fresh alkyla-tion catalyst.
BRIEF DESCRIPTION OF THE DRAWINGS
The single figure is a schematic flow diagram of the process of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Reference is now made to the accompanying draw-ing for a more detailed description of the process of the . .
1063~89 .
present invention.
Spent catalyst ~rom alkylation unit 10 passes via line 11 into distillation zone 12, the primary treatment ¦ stage of the process. The spent catalyst from alkylation unit 10 comprises primarily sulfuric acid (about 88 - 90%
by weight) and contains in addition, fluorosul~onic acid, (~ 15% by volume) water (3 - 4% by weight), acid oils, sul-fonated and fluorinated organic materials and other side reaction products formed in the alkylation reaction. Gen-erally, the total fluoride content, measured as HF, is in the range of 15,000 to 30,000 ppmw (parts per million weight)O
Distillation zone 12 is preferably operated at atmospheric pressure or below and elevated temperatures of from about 50 to about 120C. It is desirable that the distillation apparatus be of a type which can generate a large surface area of spent catalyst, one such type of preferred apparatus being a multi-stage agitated vacuum digester.
As noted above, the distillation is conducted in the presence of at least the stoichometric amount of water needed to hydrolyze the fluorosulfonic acid to hydrogen fluoride. Generally speaking, in spent alkylation catalyst the water content is from 3 to 4% by weight. Thus, in a typical spent alkylation catalyst, it is not necessary to add water to effect hydrolysis of all of the fluorosulfonic acid in the spent catalyst. As will be seen hereafter, how-ever, conducting the distillation in the presence of a stoichometric excess of water, e.g. up to 15% by weight of the spent catalyst, greatly enhances fluoride removal in the distillation zone. Accordingly, provision can be made for adding water to distillation zone 12 via line 26.
.
1063~89 -A lightJ substantially vapor fraction comprising primarily hydrogen fluoride, some fluorosulfonic acid and a small amount of S02 formed from oxidative side reactions flashes and is removed from distillation zone 12 via line 13.
The hydrogen fluoride in the fraction removed via line 13 results not only from the hydrogen fluoride originally pres-ent in the spent catalyst and that formed by hydrolysis of the fluorosulfonic acid, but in addition, arises from de-composition of alkyl fluorosulfonates and other organofluoro compounds formed in the alkylation reaction.
A second, heavier fraction comprising the resi-dual material from zone 12 and containing substantially all of the sulfuric acid present in the spent catalyst, plus residual hydrogen fluoride (preferably C lO0 ppmw HF), acid oils, water and other impurities is removed from distilla-tion zone 12 via line 14 and transferred to reaction zone 15. Reaction zone 15 is the secondary treatment stage of ` the process and conveniently employs a vessel, preferably agitated, into which is introduced a particulate silica con- -taining material via line 16. In reaction zone 15, which is preferably operated at elevated temperatures and sub-atmos-pheric pressure, the residual hydrogen fluoride present in the spent catalyst fractlon removed from distillation zone 12, reacts with the silica to form silicon fluoride. Silicon, fluoride belng more volatile than HF, is relatively easily separated from the mixture in zone 15. A substantially vapor fraction containing the silicon fluoride thus produced is removed via line 29 for disposal. Any non-reactive solids introduced wlth the silica containing material are removed from the reaction zone 15 via line 17 and sent to waste.
:
: 1063589 ,' :
An acid effluent stream containing substantially all of the sulfuric acid present in the spent catalyst and preferably having a fluoride content, as HF, of c 10 ppmw is removed from reaction zone 15 via line 18 and fed to sludge conversion unit 19. In sludge conversi~n unit 19, the spent catalyst, having a greatly reduced ~luoride con-tent, is combusted in a suitable furnace under conditions such that all the sulfur species present in the catalyst are converted to sulfur dioxide. The sludge conversion unit fur-. ,.,.~
ther contains a converter section employing an oxidation catalyst such as V205 which, in the presence of air, converts ; the S02 into S03. Part of the S03 thus produced is absorbed in a fresh sulfuric acid solution to form oleum which is then diluted with water to form 97 - 99 weight ~ sulfuric acid.
The ~ulfuric acid thus produced is removed via line 20 for recycle to alkylation unit 10.
The light fraction removed from zone 12 via line 13 and comprising hydrogen fluoride, fluorosulfonic acid and S02, is introduced into fluorosulfonic acid regeneration unit 27 and combined with S03 to convert the HF to additional fluorosulfonic acid. A portion of the S03 in unit 27 may be obtained from unit 19 via line 22. Any additional S03 needed to convert the hydrogen fluoride to fluorosulfonic acid can be obtained from S03 make-up stream 23. The regen-; erated fluorosulfonic acid stream exits unit 27 via line 28.
The S02 present in the fluorosulfonic acid stream is removed from line 28 via line 24 to provide a stream comprising sub-stantially fluorosulfonic acid. The fluorosulfonic acid is then combined with the sulfuric acid from line 20 in the proper proportions to form fresh alkylation catalyst which .~: ~ ' . ' - . .
' ' ~
is fed to alkylation unit 10 via line 25. -While reference has been made to the use of a multi-stage stirred vacuum digester in distillation zone 12, it is to be understood that other types of equipment can be employed. The purpose of the primary treatment stage or distillation zone is to remove the relatively volatile hydrogen fluoride from the spent catalyst. Thus, any means which will provide a large surface area of spent catalyst to allow efficient flashing of the hydrogen fluoride can be used. For example, rotary film evaporators, packed trickle -towers, spray towers, baffle towers, rotary disc contactors, etc. can be employed.
Preferably, the distillation zone, i.e. the pri-mary treatment stage, comprises distillation at atmospheric pressure or below and at elevated temperatures. Pressures in the distillation zone should be as low as economically prac-tical and preferably below about 1 psia. Temperatures will, of course, depend on the pressures, but generally will range from about 50 to about 120C., and preferably from about ~-80 to 110C. It has been found that if the spent alkylation catalyst is sub~ected to temperatures of 125C. or higher for e~tended periods of time, the catalyst tends to thicken to a semi-solid mass. Thus, the temperatures should be .,, kept below about 125C. For a typical spent alkylation catalyst containing 20,000 to 30,000 ppmw fluoride as HF, it has been found that if the distillation zone is maintained . . .
at a temperature of around 100C. and a pressure of about or below 1 psia, and under conditions affording increased surface a~b-aiof thb spent catalyst, 90% recovery~ by weight, 3 of the fluoride (calculated as HF) can be achieved without : g :.
' ~ .
. ~ ~
1063~89 adverse degradation side reactions which occur at higher temperatures.
The residence time in the distillation zone will vary depending on pressure, temperature, fluoride content of the spent acid, water content, etc. Generally speaking, the residence time of the spent catalyst in the distillation zone should be sufficient to permit maximum hydrolysis of the fluorosulfonic acid to hydrogen fluoride and subsequent flashing of the hydrogen fluoride and/or remaining fluoro-sulfonic acid from the distillation zone. Additionally, relatively long residence times in the distillation zone promote the decomposition of organofluoro compounds in the spent catalyst into hydrogen fluoride and/or fluorosulfonic acid thereby maximizing the recovery of the fluorosulfonic acid for recycle to the alkylation unit and minimizing the fluoride removal needed in the second stage of the process.
However, while long residence times increase the fluoride recovery from the spent catalyst in the distilla-tion zone, there is also a concomitant increase in the amount Of S02 recovered in the vapor fraction with the hydrogen fluoride. Since S02 losses represent loss of sulfur for regeneration into fresh sulfuric acid, minimum digestion or residence time in the distillation zone consistent with adequate fluoride removal should be used so as to minimize such losses. In general, it has been found that at a tem-perature of about 100C. and a pressure of about 1 psia or lower, a residence time of 4 hours or greater wlll effect -~ removal of 90% by weight of the total fluoride, calculated as HF, from a typical spent catalyst, i.e. containing 20,000 _ 30,000 ppmw fluoride. In such a typical spent catalyst, .
1063~89 if the digestion time is increased to ~ hours or greater, as for example, from about 6 to about 8 hours, greater fluoride removal (about 97% by weight) can be obtained, e.g. from about 23,000 ppmw to about 700 - 800 ppmw. It has also been found that if the spent catalyst has a rela-tively low initial fluoride concentration, e.g. about 1000 - 1500 ppmw, calculated as HF, the fluoride level can be reduced to 74 ppmw after 2 hours and 33 ppmw after 8 hours.
With ample residence time and at a temperature of around 100C. and a pressure of 5 - 15 mm. Hg, the fluoride content (as HF) of a typical spent acid catalyst can be reduced to 100 ppmw or less.
While the distillation step of the process of the present invention can be conducted in the presence of the amount of water needed to stoichometrically react with the fluorosulfonic acid to form hydrogen fluoride, it has been found that higher water content in the spent catalyst greatly improves fluoride recovery in the distillation zone.
As noted, typical spent catalyst contains 3 - 4% by weight water which is sufficient, as noted above, to effect good - recovery of fluoride from spent catalyst in the distillation zone. However, when the water content of the spent catalyst contains up to 8% by weight water, and more preferably from about 8 to about 15% by weight water, the volatility of the fluorides in the s~ent acid is greatly increased. Apparently, - the excess water is needed to (1) force the hydrolysis of the fluorosulfonic acid to HF which is more volatile, and/or
(2) reduce the solubility of the HF in the spent acid cata-lyst. Indeed, the presence of approximately 15 weight %
water in the spent catalyst will permit reduction of the ' ' ~
.
' . ' ~ ~ , .
106358g fluoride content (calculated as HF) ~rom around 24,000 ppmw, to about 50 ppmw a~ter only 8 hours residence time in the distillation zone.
It is also possible to employ inert gas purging or stripping of the spent acid catalyst in the distillation zone. Thus, purge gases such as N2, argon, helium, etc.
could be used. Moreover, steam stripping could be employed, the steam serving the added purpose of supplying water to the system.
In the secondary treatment stage of the process of the present invention, the residual hydrogen fluoride in the spent catalyst is contacted with a silica containing material in an amount and for a period of time sufficient to convert at least a portion of the hydrogen fluoride to silicon fluoride which being more volatile than HF, is more easily separated from the spent catalyst. Virtually any material containing silica can be used. The term silica, as used herein, refers to the compound SiO2 in anhydrous or hydrated form. The silica containing material can be either substan-tially pure silica, e.g. pure SiO2~ or any one of numerous naturally occurring substances such as glass, quartz, sand, ~lint, diatomite, various silicates, etc. Materials such as silica gel and fumed silica which have high surface area are quite desirable.
The amount of silica as SiO2 which must be used in the reaction zone to effect removal of the residual HF
can vary substantially, but preferably will be present in at least an amount, by weight, to stoichometrically react with the residual HF. ~mounts larger than the stoichometric-ally needed amount are especially desirable since shorter ' :
~063~89 residence times in the react~on zone can be used.
The total amount of silica containing material - used in the reaction zone will vary depending upon the fluoride content of the spent acid catalyst, the silica content of the material, temperature conditions, contact times, surface area of the silica containing material, etc However, in general, the amount, by weight, of silica con-taining material used will be such as to provide an amount of silica to stoichometrically react with the residual HF.
Larger amounts of silica containing material containing the stoichometric amount of silica, reduce the time in the reaction zone and therefore, are especially desirable. It should be observed that the silica containing material charged to the reaction zone can be used until it completely reacts with the HF to form silicon fluoride. The silicon fluoride being volatile is easily removed, leaving no reaction products deposited on the remaining silica to impede further reactlon. It will be apparent that to effect efficient removal of the residual hydrogen fluoride in the spent cata-lyst fraction in the reaction zone, there must be sufficient contact time between the spent catalyst and the silica. The actual contact or residence time required will depend upon several variables, such as for example, particle size of the silica containing material, the silica content of the material, surface area of the material~ the fluoride content -;~ of the catalyst, the temperature, etc. Accordingly, no specific residence time can be stated. However, it has ~, generally been found that when the contacting is carried out at an elevated temperature as, for example, approximately 100C., a residence time of about 4 hours or greater, is !
1063~89 :
required to o~tain maximum reduction in the fluoride level.
While the particle size of the silica containing i material is not critical, because of increased surface area, materials of relatively fine particle size, e.g. < 100 microns, ; are generally pre~erred. Silica containing materials of such a particle size have surface areas of 100 m2/g and greater, thus providing much greater contact area for reaction of the hydrogen fluoride with the silica. However, while a silica containing material of relatively large particle size, e.g.
~ 100 microns may require a longer residence time to effect the desired reduction in the fluoride content, such material ; will work satisfactorily. Since large surface areas of the silica containing material enhance the fluoride removal, materials such as silica gel and fumed silica which generally ;l have extremely high surface areas make desirable materials , ~ for use in the reaction zone.
; L `
l Preferably the reaction zone is operated at , j elevated temperatures, the rate of reaction of the hydrogen fluoride with the silica being enhanced at elevated tempera-~r tures. Generally speaking, a temperature in the range of : from about 50 to about 120C. promotes efficient reaction -~
between the hydrogen fluoride and the silica, a temperature in the range of from about 90 to about 110C. being parti-'~! .
`; oularly desirable.
i ~ ,, .
Pressures in the reaction zone should be low .. ..
` enough to permit good volatilization or distillation of the , silicon fluoride. Generally, then, the pressures in the <~ reaction zone will be below atmospheric, and preferably about 1 psia or lower.
To aid in flashing the silicon fluoride from the '- . .
:
1063~89 ~ . .
reaction zone, inert sweep or purge gas streams can be used. Typical gases include N2, helium, argon, etc.
As described above, the process of the present -invention also provides a method for regeneration of fresh alkylation catalysts. The hydrogen fluoride which is removed in the primary treatment stage can be reacted with sulfur trioxide to form fluorosulfonic acid which together with the fluorosulfonic acid removed in the distillation zone can be employed as one of the components of fresh alkylation catalyst. Likewise, the substantially fluoride free spent acid fed to the sludge conversion unit is ultimately used to generate fresh sulfuric acid, thus providing the other component of the alkylation catalyst. The sludge conversion unit can also provide at least a portion of the sulfur trioxide -- used to react with the hydrogen fluorlde recovered from the primary treatment stage to form the fluorosulfonic acid.
In forming the fresh alkylation catalyst, the fluorosulfonic and sulfuric acids are combined in a weight ratio of from about 0.11/1 to about 0.32/1, respectively, to form an acid catalyst. The fresh catalyst may, in addition, contain up ` to 3% by weight water.
The process of the present invention not only provides an efficient method for the recovery of the fluoro-sulfonic acid from the spent alkylation catalyst, but in addition, provides a feed for the sludge conversion unit which is substantially free of deleterious amounts of fluoride. As .- ~ .
~ previously noted, the sludge conversion unit employs a re-:
fractory lined furnace which is readily attacked by hydrogen fluoride. Accordingly, to avoid damage to the refractory, it is necessary that the hydrogen fluoride content of the feed " ' . .
.
.
, 1063~89 be reduced as much as possible, if not eliminated. Addi-tionally, removal of the fluoride from the spent acid ensures that the sulfur dioxide produced in the sludge conversion unit will be substantially free of fluoride compounds which could volatilize the vanadium in the V2O5 oxidation catalyst used to convert the SO2 to SO3.
To further illustrate the advantages of the - present invention~ the following non-limiting examples arepresented. All fluoride contents are by weight and calculated as HF unless otherwise indicated.
Example I
- A 200 ml. sample of spent alkylation acid catalyst ~ containing 23,600 ppm fluoride was placed in a one-liter ; stirred reactor maintained at 100C. and 5 - 15 ~m. Hg abso- ;
lute pressure for 8.5 hours, the evolving HF and HFS03 being collected. Periodic analysis of the spen acid catalyst showed 40% of the fluoride had been removêd after 4 hours, a fluoride content residual of 1530 ppm after 6.5 hours, and 780 ppm after 8.5 hours.
Example II
The procedure of Example I was followed except the spent alkylation catalyst was admixed with an amount of water equal to 5% by weight of the spent acid catalyst in the reactor which brought the total water content of the spent acld catalyst to about 8 - 9% by weight. It was found that after 8 hours of digestion (distillation), the spent acid catalyst had a residual fluoride content of 450 ppm.
Example III
The procedure of Example II was followed with the exception that an amount of water equal to 10 weight %
' . .
.
' 1063~89 :
of the spent acid catalyst was added bringlng the total water content of the spent catalyst in the reactor to about 13 - 14%. It was found that after 8 hours o~ digestion, the spent acid catalyst had a residual fluoride content of 50 ppm.
Example IV
A 14 g. sample of residual spent acid obtained as per the general procedure of Example I and containing 17,800 ppm ~luoride was stirred with a 28.2g charge of l/8"
diameter glass beads at 150C. for 22 hours and 25 mm. Hg absolute pressure. The evolving silicon fluoride was dis-carded. Analyses of the effluent acid showed a fluoride con-centration of 47 ppm.
Example V
A 29.2 g. sample of residual spent acid obtained as per the general procedure of ~xample I and containlng 363 ppm fluoride was heated in the presence of 2.3 g. of glass wool for 4 hours at 100C. and 30 mm. Hg absolute pressure~
the evolving silicon fluoride being discarded. The fluoride level of the sample was reduced to 77 ppm.
Example VI
A 30.6 g. sample of residual spent acid obtained as per the general procedure of Example I and containing 768 ppm fluoride was heated in the presence of 12.4 g. of lO-30 mesh sand for 5 hours at 105 - 110C. and 70 mm. Hg abso-lute pressure. A slow N2 purge was used during the reaction to sweep the silicon fluoride from the reaction mixture.
Analysis of the residual acid showed a fluoride content of 26 ppm.
Example VII
Approximately 200 ml. of spent alkylation catalyst 1063~89 .
which had been subjected to the primary distillation step and containing 21 ppm fluoride was mixed with 10 ml. of 80 -120 mesh sand and heated for 6 hours at 100C. and 10 mm. Hg absolute pressure. The residual fluoride content of the treated spent catalyst was found to be 17 ppm.
ExampIe YIII
Distillates obtained following the general pro-cedure of Example I from two samples of spent acid were col-lected in a liquid N2 cooled trap, warmed to 0C., and mixed with liquid SO3. The resulting solutions were distilled at reduced pressure to purify the fluorosulfonic acid. The data for regeneration Of the fluorosulfonic acid is given in Table I below.
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td O ~ :~ O c) O ^ rn ~ ~ + ~ r~
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1063~89 As can be seen from the data above, the process of the present invention provides an efficient method for the removal of fluoro compounds from spent alkylation cata-lyst. With reference to Examples I - III, it can be seen that the distillation step effects substantial removal of the fluoro compounds from the spent catalyst. As can be seen from Examples IV - VII, the secondary treatment stage provides a spent acid catalyst free from substantial amounts of fluoro compounds.
With reference to Éxample VIII, it is to be ob-served that the process herein provides an efficient method of regenerating fluorosulfonic acid from the spent catalyst.
Note that overall fluoride balances of 75 and 85% were ob-served for the two runs.
It can be seen that by employing the process of ~ ;
the present invention, potential damage to the refractory lining ln the furnace of the sludge conversion unit, and any loss of the V205 oxldation catalyst by fluoride vaporization of the vanadium can be virtually eliminated.
The present invention has been described with reference to several specific embodiments thereof, and accordingly, it will be apparent that many modifications, substitutions~ and omissions will be readily suggested to a person of ordinary skill in the art without departing from the spirit of the present invention. Therefore, it is to be understood that the scope of the invention is to be determined solely by the claims appended hereto.
- 20 ~
.
.
~ .
water in the spent catalyst will permit reduction of the ' ' ~
.
' . ' ~ ~ , .
106358g fluoride content (calculated as HF) ~rom around 24,000 ppmw, to about 50 ppmw a~ter only 8 hours residence time in the distillation zone.
It is also possible to employ inert gas purging or stripping of the spent acid catalyst in the distillation zone. Thus, purge gases such as N2, argon, helium, etc.
could be used. Moreover, steam stripping could be employed, the steam serving the added purpose of supplying water to the system.
In the secondary treatment stage of the process of the present invention, the residual hydrogen fluoride in the spent catalyst is contacted with a silica containing material in an amount and for a period of time sufficient to convert at least a portion of the hydrogen fluoride to silicon fluoride which being more volatile than HF, is more easily separated from the spent catalyst. Virtually any material containing silica can be used. The term silica, as used herein, refers to the compound SiO2 in anhydrous or hydrated form. The silica containing material can be either substan-tially pure silica, e.g. pure SiO2~ or any one of numerous naturally occurring substances such as glass, quartz, sand, ~lint, diatomite, various silicates, etc. Materials such as silica gel and fumed silica which have high surface area are quite desirable.
The amount of silica as SiO2 which must be used in the reaction zone to effect removal of the residual HF
can vary substantially, but preferably will be present in at least an amount, by weight, to stoichometrically react with the residual HF. ~mounts larger than the stoichometric-ally needed amount are especially desirable since shorter ' :
~063~89 residence times in the react~on zone can be used.
The total amount of silica containing material - used in the reaction zone will vary depending upon the fluoride content of the spent acid catalyst, the silica content of the material, temperature conditions, contact times, surface area of the silica containing material, etc However, in general, the amount, by weight, of silica con-taining material used will be such as to provide an amount of silica to stoichometrically react with the residual HF.
Larger amounts of silica containing material containing the stoichometric amount of silica, reduce the time in the reaction zone and therefore, are especially desirable. It should be observed that the silica containing material charged to the reaction zone can be used until it completely reacts with the HF to form silicon fluoride. The silicon fluoride being volatile is easily removed, leaving no reaction products deposited on the remaining silica to impede further reactlon. It will be apparent that to effect efficient removal of the residual hydrogen fluoride in the spent cata-lyst fraction in the reaction zone, there must be sufficient contact time between the spent catalyst and the silica. The actual contact or residence time required will depend upon several variables, such as for example, particle size of the silica containing material, the silica content of the material, surface area of the material~ the fluoride content -;~ of the catalyst, the temperature, etc. Accordingly, no specific residence time can be stated. However, it has ~, generally been found that when the contacting is carried out at an elevated temperature as, for example, approximately 100C., a residence time of about 4 hours or greater, is !
1063~89 :
required to o~tain maximum reduction in the fluoride level.
While the particle size of the silica containing i material is not critical, because of increased surface area, materials of relatively fine particle size, e.g. < 100 microns, ; are generally pre~erred. Silica containing materials of such a particle size have surface areas of 100 m2/g and greater, thus providing much greater contact area for reaction of the hydrogen fluoride with the silica. However, while a silica containing material of relatively large particle size, e.g.
~ 100 microns may require a longer residence time to effect the desired reduction in the fluoride content, such material ; will work satisfactorily. Since large surface areas of the silica containing material enhance the fluoride removal, materials such as silica gel and fumed silica which generally ;l have extremely high surface areas make desirable materials , ~ for use in the reaction zone.
; L `
l Preferably the reaction zone is operated at , j elevated temperatures, the rate of reaction of the hydrogen fluoride with the silica being enhanced at elevated tempera-~r tures. Generally speaking, a temperature in the range of : from about 50 to about 120C. promotes efficient reaction -~
between the hydrogen fluoride and the silica, a temperature in the range of from about 90 to about 110C. being parti-'~! .
`; oularly desirable.
i ~ ,, .
Pressures in the reaction zone should be low .. ..
` enough to permit good volatilization or distillation of the , silicon fluoride. Generally, then, the pressures in the <~ reaction zone will be below atmospheric, and preferably about 1 psia or lower.
To aid in flashing the silicon fluoride from the '- . .
:
1063~89 ~ . .
reaction zone, inert sweep or purge gas streams can be used. Typical gases include N2, helium, argon, etc.
As described above, the process of the present -invention also provides a method for regeneration of fresh alkylation catalysts. The hydrogen fluoride which is removed in the primary treatment stage can be reacted with sulfur trioxide to form fluorosulfonic acid which together with the fluorosulfonic acid removed in the distillation zone can be employed as one of the components of fresh alkylation catalyst. Likewise, the substantially fluoride free spent acid fed to the sludge conversion unit is ultimately used to generate fresh sulfuric acid, thus providing the other component of the alkylation catalyst. The sludge conversion unit can also provide at least a portion of the sulfur trioxide -- used to react with the hydrogen fluorlde recovered from the primary treatment stage to form the fluorosulfonic acid.
In forming the fresh alkylation catalyst, the fluorosulfonic and sulfuric acids are combined in a weight ratio of from about 0.11/1 to about 0.32/1, respectively, to form an acid catalyst. The fresh catalyst may, in addition, contain up ` to 3% by weight water.
The process of the present invention not only provides an efficient method for the recovery of the fluoro-sulfonic acid from the spent alkylation catalyst, but in addition, provides a feed for the sludge conversion unit which is substantially free of deleterious amounts of fluoride. As .- ~ .
~ previously noted, the sludge conversion unit employs a re-:
fractory lined furnace which is readily attacked by hydrogen fluoride. Accordingly, to avoid damage to the refractory, it is necessary that the hydrogen fluoride content of the feed " ' . .
.
.
, 1063~89 be reduced as much as possible, if not eliminated. Addi-tionally, removal of the fluoride from the spent acid ensures that the sulfur dioxide produced in the sludge conversion unit will be substantially free of fluoride compounds which could volatilize the vanadium in the V2O5 oxidation catalyst used to convert the SO2 to SO3.
To further illustrate the advantages of the - present invention~ the following non-limiting examples arepresented. All fluoride contents are by weight and calculated as HF unless otherwise indicated.
Example I
- A 200 ml. sample of spent alkylation acid catalyst ~ containing 23,600 ppm fluoride was placed in a one-liter ; stirred reactor maintained at 100C. and 5 - 15 ~m. Hg abso- ;
lute pressure for 8.5 hours, the evolving HF and HFS03 being collected. Periodic analysis of the spen acid catalyst showed 40% of the fluoride had been removêd after 4 hours, a fluoride content residual of 1530 ppm after 6.5 hours, and 780 ppm after 8.5 hours.
Example II
The procedure of Example I was followed except the spent alkylation catalyst was admixed with an amount of water equal to 5% by weight of the spent acid catalyst in the reactor which brought the total water content of the spent acld catalyst to about 8 - 9% by weight. It was found that after 8 hours of digestion (distillation), the spent acid catalyst had a residual fluoride content of 450 ppm.
Example III
The procedure of Example II was followed with the exception that an amount of water equal to 10 weight %
' . .
.
' 1063~89 :
of the spent acid catalyst was added bringlng the total water content of the spent catalyst in the reactor to about 13 - 14%. It was found that after 8 hours o~ digestion, the spent acid catalyst had a residual fluoride content of 50 ppm.
Example IV
A 14 g. sample of residual spent acid obtained as per the general procedure of Example I and containing 17,800 ppm ~luoride was stirred with a 28.2g charge of l/8"
diameter glass beads at 150C. for 22 hours and 25 mm. Hg absolute pressure. The evolving silicon fluoride was dis-carded. Analyses of the effluent acid showed a fluoride con-centration of 47 ppm.
Example V
A 29.2 g. sample of residual spent acid obtained as per the general procedure of ~xample I and containlng 363 ppm fluoride was heated in the presence of 2.3 g. of glass wool for 4 hours at 100C. and 30 mm. Hg absolute pressure~
the evolving silicon fluoride being discarded. The fluoride level of the sample was reduced to 77 ppm.
Example VI
A 30.6 g. sample of residual spent acid obtained as per the general procedure of Example I and containing 768 ppm fluoride was heated in the presence of 12.4 g. of lO-30 mesh sand for 5 hours at 105 - 110C. and 70 mm. Hg abso-lute pressure. A slow N2 purge was used during the reaction to sweep the silicon fluoride from the reaction mixture.
Analysis of the residual acid showed a fluoride content of 26 ppm.
Example VII
Approximately 200 ml. of spent alkylation catalyst 1063~89 .
which had been subjected to the primary distillation step and containing 21 ppm fluoride was mixed with 10 ml. of 80 -120 mesh sand and heated for 6 hours at 100C. and 10 mm. Hg absolute pressure. The residual fluoride content of the treated spent catalyst was found to be 17 ppm.
ExampIe YIII
Distillates obtained following the general pro-cedure of Example I from two samples of spent acid were col-lected in a liquid N2 cooled trap, warmed to 0C., and mixed with liquid SO3. The resulting solutions were distilled at reduced pressure to purify the fluorosulfonic acid. The data for regeneration Of the fluorosulfonic acid is given in Table I below.
' ., :
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1063~89 As can be seen from the data above, the process of the present invention provides an efficient method for the removal of fluoro compounds from spent alkylation cata-lyst. With reference to Examples I - III, it can be seen that the distillation step effects substantial removal of the fluoro compounds from the spent catalyst. As can be seen from Examples IV - VII, the secondary treatment stage provides a spent acid catalyst free from substantial amounts of fluoro compounds.
With reference to Éxample VIII, it is to be ob-served that the process herein provides an efficient method of regenerating fluorosulfonic acid from the spent catalyst.
Note that overall fluoride balances of 75 and 85% were ob-served for the two runs.
It can be seen that by employing the process of ~ ;
the present invention, potential damage to the refractory lining ln the furnace of the sludge conversion unit, and any loss of the V205 oxldation catalyst by fluoride vaporization of the vanadium can be virtually eliminated.
The present invention has been described with reference to several specific embodiments thereof, and accordingly, it will be apparent that many modifications, substitutions~ and omissions will be readily suggested to a person of ordinary skill in the art without departing from the spirit of the present invention. Therefore, it is to be understood that the scope of the invention is to be determined solely by the claims appended hereto.
- 20 ~
.
.
~ .
Claims (26)
1. A process for the removal of fluoride compounds from spent alkylation catalyst containing fluorosulfonic acid and sulfuric acid comprising:
(a) subjecting said spent catalyst to distil-lation, at atmospheric pressure or below, in a temperature range of from about 50 to about 120°C. and in admixture with at least the stoichometric amount of water necessary to hydrolyze said fluorosulfonic acid to hydrogen fluoride;
(b) recovering a first fraction from said distillation, said first fraction comprising primarily hydrogen fluoride;
(c) recovering a second fraction from said distillation, said second fraction comprising residual hydro-gen fluoride and the greater part of said sulfuric acid present in said spent catalyst;
(d) contacting, in a reaction zone, said second fraction with a silica containing material in an amount and for a period of time sufficient to react at least a portion of said residual hydrogen fluoride with said silica to form silicon fluoride;
(e) volatilizing said silicon fluoride from said reaction zone; and (f) recovering from said reaction zone an effluent acid fraction containing the greater part of said sulfuric acid present in said spent catalyst and being free of substantial amounts of fluoride compounds.
(a) subjecting said spent catalyst to distil-lation, at atmospheric pressure or below, in a temperature range of from about 50 to about 120°C. and in admixture with at least the stoichometric amount of water necessary to hydrolyze said fluorosulfonic acid to hydrogen fluoride;
(b) recovering a first fraction from said distillation, said first fraction comprising primarily hydrogen fluoride;
(c) recovering a second fraction from said distillation, said second fraction comprising residual hydro-gen fluoride and the greater part of said sulfuric acid present in said spent catalyst;
(d) contacting, in a reaction zone, said second fraction with a silica containing material in an amount and for a period of time sufficient to react at least a portion of said residual hydrogen fluoride with said silica to form silicon fluoride;
(e) volatilizing said silicon fluoride from said reaction zone; and (f) recovering from said reaction zone an effluent acid fraction containing the greater part of said sulfuric acid present in said spent catalyst and being free of substantial amounts of fluoride compounds.
2. The process of claim l wherein said distilla-tion is conducted for a period of time sufficient to effect at least partial decomposition of at least some organofluoro compounds in said spent catalyst into hydrogen fluoride and/or fluorosulfonic acid.
3. The process of claim 1 wherein said distil-lation is conducted under conditions affording increased surface area of said spent catalyst.
4. The process of claim 1 wherein said distil-lation is conducted at a pressure of about 1 psia or lower and a temperature in the range of from about 80 to about 110°C.
5. The process of claim 4 wherein said distil-lation is conducted in the presence of from about 3 to about 8% by weight water.
6. The process of claim 4 wherein said distil-lation is conducted in the presence of from about 8 to about 15% by weight water.
7. The process of claim 6 wherein said spent catalyst is subjected to said distillation at a temperature of about 100°C. and for a period of time such that said second fraction has a fluoride content of about 100 ppmw or less calculated as hydrogen fluoride.
8. The process of claim 4 wherein said spent catalyst is subjected to said distillation for a period of 4 hours or greater.
9. The process of claim 4 wherein said distil-lation of said spent catalyst is conducted at a temperature of about 100°C. in admixture with from about 8 to about 15%
by weight water.
by weight water.
10. The process of claim 1 wherein said contact-ing in said reaction zone is conducted at a temperature in the range of from about 50 to about 120°C. and at sub-atmospheric pressure.
11. The process of claim 10 wherein said contact-ing is carried out for a period of about 4 hours or greater.
12. The process of claim 10 wherein said silica containing material has a silica content, by weight, of about at least the stoichometric amount necessary to convert said residual hydrogen fluoride to silicon fluoride.
13. The process of claim 12 wherein said contact-ing is conducted at a pressure of about 1 psia or lower.
14. The process of claim 9 wherein said contacting in said reaction zone is conducted at a temperature of about 90 to about 110°C., at a pressure of about 1 psia or lower, in the presence of a silica containing material having a silica content, by weight, of at least the stoichometric amount necessary to convert said residual hydrogen fluoride to silicon fluoride.
15. A process for the regeneration of spent alkylation catalyst containing fluorosulfonic acid and sul-furic acid comprising:
(a) subjecting said spent catalyst to distil-lation, at atmospheric pressure or below, in a temperature range of from about 50 to about 120°C. and in admixture with at least the stoichometric amount of water necessary to hydrolyze said fluorosulfonic acid to hydrogen flouride;
(b) recovering a first fraction from said distillation, said first fraction comprising primarily hydrogen flouride;
(c) treating said first fraction with sul-fur trioxide to form regenerated fluorosulfonic acid from said hydrogen flouride present in said first fraction;
(d) recovering a second fraction from said distillation, said second fraction comprising residual hydro-gen flouride and the greater part of said sulfuric acid present in said spent catalyst;
(e) contacting, in a reaction zone, said second fraction with a silica containing material in an amount and for a period of time sufficient to react at least a por-lion of said residual hydrogen flouride with said silica to form silicon flouride;
(f) volatilizing said silicon flouride from said reaction zone;
(g) recovering from said reaction zone an effluent acid fraction containing the greater part of said sulfuric acid present in said spent catalyst and being free of substantial amounts of flouride compounds;
(h) combusting said effluent acid fraction to convert said sulfuric acid to sulfur dioxide;
(i) converting at least a portion of said sulfur dioxide to sulfur trioxide;
(j) converting at least a portion of said sulfur trioxide from step (i) into regenerated sulfuric acid; and (k) combining said regenerated sulfuric acid with said regenerated fluorosulfonic acid to produce fresh alkylation catalyst.
(a) subjecting said spent catalyst to distil-lation, at atmospheric pressure or below, in a temperature range of from about 50 to about 120°C. and in admixture with at least the stoichometric amount of water necessary to hydrolyze said fluorosulfonic acid to hydrogen flouride;
(b) recovering a first fraction from said distillation, said first fraction comprising primarily hydrogen flouride;
(c) treating said first fraction with sul-fur trioxide to form regenerated fluorosulfonic acid from said hydrogen flouride present in said first fraction;
(d) recovering a second fraction from said distillation, said second fraction comprising residual hydro-gen flouride and the greater part of said sulfuric acid present in said spent catalyst;
(e) contacting, in a reaction zone, said second fraction with a silica containing material in an amount and for a period of time sufficient to react at least a por-lion of said residual hydrogen flouride with said silica to form silicon flouride;
(f) volatilizing said silicon flouride from said reaction zone;
(g) recovering from said reaction zone an effluent acid fraction containing the greater part of said sulfuric acid present in said spent catalyst and being free of substantial amounts of flouride compounds;
(h) combusting said effluent acid fraction to convert said sulfuric acid to sulfur dioxide;
(i) converting at least a portion of said sulfur dioxide to sulfur trioxide;
(j) converting at least a portion of said sulfur trioxide from step (i) into regenerated sulfuric acid; and (k) combining said regenerated sulfuric acid with said regenerated fluorosulfonic acid to produce fresh alkylation catalyst.
16. The process of claim 15 wherein said distil-lation is conducted at a pressure of about 1 psia or lower and a temperature in the range of from about 80 to about 110°C.
17. The process of claim 16 wherein said distil-lation is conducted in the presence of from about 3 to about 8% by weight water.
18. The process of claim 16 wherein said distil-lation is conducted in the presence of from about 8 to about 15% by weight water.
19. The process of claim 16 wherein said distil-lation of said spent catalyst is conducted at a temperature of about 100°C. in admixture with from about 8 to about 15%
by weight water.
by weight water.
20. The process of claim 15 wherein said contacting in said reaction zone is conducted at a temperature in the range of from about 50 to about 120°C and at sub-atmospheric pressure.
21. The process of claim 20 wherein said contacting is carried out for a period of about 4 hours or greater.
22. The process of claim 20 wherein said silica containing material has a silica content, by weight, of about at least the stoichometric amount necessary to convert said residual hydrogen fluoride to silicon fluoride.
23. The process of claim 22 wherein said contacting is conducted at a pressure of about 1 psia or lower.
24. The process of claim 19 wherein said contact-ing in said reaction zone is conducted at a temperature of about 90 to about 110°C., at a pressure of about 1 psia or lower, in the presence of a silica containing material having a silica content, by weight, of at least the stoichometric amount necessary to convert said residual hydrogen fluoride to silicon fluoride.
25. The process of claim 15 wherein at least a portion of the sulfur trioxide used in step (c) is that ob-tained in step (i).
26. The process of claim 15 wherein said regener-ated fluorosulfonic acid and said regenerated sulfuric acid are combined in a weight ratio of about 0.11/1 to about 0.32/1 to produce said fresh alkylation catalyst.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US05/537,505 US3976759A (en) | 1974-12-30 | 1974-12-30 | Process for removal of fluoride compounds from spent alkylation catalyst |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1063589A true CA1063589A (en) | 1979-10-02 |
Family
ID=24142928
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA235,599A Expired CA1063589A (en) | 1974-12-30 | 1975-09-16 | Alkylation catalyst recovery process |
Country Status (2)
| Country | Link |
|---|---|
| US (1) | US3976759A (en) |
| CA (1) | CA1063589A (en) |
Families Citing this family (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4033899A (en) * | 1974-12-30 | 1977-07-05 | Texaco Inc. | Alkylation fluosulfonic-sulfuric acid catalyst recovery process with silica-alumina removal of fluoride compounds |
| DE2928598C2 (en) * | 1979-07-14 | 1984-01-19 | Hoechst Ag, 6230 Frankfurt | Methods for cleaning up waste sulfuric acid containing fluoride |
| FR2480019B1 (en) * | 1980-04-08 | 1986-11-14 | Etu En Nucleaire Centre | PROCESS FOR EXTRACTING FLUORIDE IONS FROM A NUCLEAR FUEL SOLUTION |
| US4395356A (en) * | 1980-11-28 | 1983-07-26 | Shell Oil Company | Method for removing catalyst residues from solutions of poly-1-butene |
| US4479926A (en) * | 1983-12-19 | 1984-10-30 | Exxon Research & Engineering Co. | Treatment of residual bottoms from fluorosulfuric acid regeneration |
| US5245100A (en) * | 1989-12-18 | 1993-09-14 | Haldor Topsoe, S.A. | Alkylation process |
| DK168520B1 (en) * | 1989-12-18 | 1994-04-11 | Topsoe Haldor As | Process for liquid phase alkylation of a hydrocarbon with an olefin alkylating agent |
| CA2031229C (en) * | 1990-11-30 | 2000-08-08 | Lynda G. Sturgeoff | Fluoride removal from sulphuric acid |
| RU2399607C2 (en) * | 2006-04-03 | 2010-09-20 | Е.И.Дюпон Де Немур Энд Компани | Selectively reacting olefins containing terminal cf2 group in mixture |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR741966A (en) * | 1931-09-02 | 1933-02-23 | ||
| US2507605A (en) * | 1946-03-14 | 1950-05-16 | Allied Chem & Dye Corp | Manufacture of hydrogen fluoride |
| US2526776A (en) * | 1948-10-19 | 1950-10-24 | Allied Chem & Dye Corp | Removal of hydrogen fluoride and silicon tetrafluoride from gases |
| US3199952A (en) * | 1960-07-21 | 1965-08-10 | Edison Soc | Process for the production of high strength, high purity hydrofluoric acid |
| US3677701A (en) * | 1970-06-01 | 1972-07-18 | Clinton A Hollingsworth | Sulfuric acid defluorination |
-
1974
- 1974-12-30 US US05/537,505 patent/US3976759A/en not_active Expired - Lifetime
-
1975
- 1975-09-16 CA CA235,599A patent/CA1063589A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| US3976759A (en) | 1976-08-24 |
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